In motor vehicles where there is a need to cool the engine or automatic transmission oil, it is common practice to add an oil cooler that is mounted in either the inlet or outlet tank of the engine radiator. There heat from the oil is transferred to the coolant for rejection in the radiator core to ambient air. Such coolers are typically constructed of tubes formed from flat plates with tubulators or extended surface provided therein. The coolant either leaves the radiator core (tubes) and flows past the oil cooler tubes in the outlet tank or flows first past the oil cooler in the inlet tank and then through the radiator core. And when more oil cooling capacity is needed, the number of oil cooler tubes (pairs of tube plates) is increased. It would, therefore, be advantageous if the capacity could be increased without having to add such parts.